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Factors affecting oxygen concentration gradients across articular cartilage
Author(s) -
Zhou Shengda,
Cui Zhanfeng,
Urban Jill P.G.
Publication year - 2004
Publication title -
international journal of experimental pathology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.671
H-Index - 72
eISSN - 1365-2613
pISSN - 0959-9673
DOI - 10.1111/j.0959-9673.2004.369ap.x
Subject(s) - oxygen , oxygen tension , limiting oxygen concentration , cartilage , chemistry , chondrocyte , respiration , clark electrode , in vivo , biophysics , anatomy , biology , electrode , microbiology and biotechnology , organic chemistry , electrolyte
Although it is commonly stated that oxygen concentrations fall to below 1% oxygen in the deep zone of articular cartilage, the evidence for this is sketchy and there is little information on the oxygen concentrations found in cartilage in vivo . The oxygen levels could be important as a number of studies have showed that low oxygen concentrations affect cartilage metabolism adversely (Grimshaw & Mason 2000; Lee & Urban 1997). As an initial step in determining oxygen concentration profiles across cartilage, we have measured the rate of oxygen consumption by chondrocytes. We then used this information to calculate the effect of various factors, such as presence of serum, cell density and perfusion from the subchondral bone on oxygen gradients across the joint. Methods Chondrocytes were isolated from the metacarpal–phalangeal joint of adult steers and cultured for 7 days in alginate beads. The rate of oxygen consumption was measured in a respiration chamber using an oxygen electrode. The effect of oxygen tension, time in culture and serum addition on oxygen consumption was investigated. This data was used to predict the oxygen tension profiles across articular cartilage. The variation in oxygen tension with distance across the joint was predicted by solving a one‐dimensional reaction–diffusion equation using a finite‐difference method. The effect of influx of oxygen from the subchondral bone on oxygen profiles was estimated. Results Oxygen consumption rates were significantly (2.5 fold) greater on the first day after isolation; on the second and subsequent days of culture, rates were similar to those reported by others ( c. 10 nmol. million cells −1 h −1 ) (Bywaters 1937). The presence of serum increased the rate by around 50%. The consumption rate was relatively independent of oxygen tension between 5 and 21% oxygen, but below 5% oxygen, consumption rates fell in a concentration‐dependent manner. Calculations of the oxygen profile across cartilage showed that the concentration was sensitive to consumption rate and was also critically dependent on the extent of supply from the subchondral bone. Calculations also showed that growth factor addition led to a fall in oxygen tension throughout the tissue. Discussion Here, we show that oxygen concentration profiles across cartilage are affected by cellular metabolic rates; addition of serum or growth factors for instance, by increasing consumption rates, can lower oxygen concentrations within the tissue significantly. Transport from the subchondral bone can also strongly affect the profile of oxygen across cartilage. Although its influence is usually ignored, there is anatomical and MRI evidence (Bashir et al . 1997) that this transport route is significant. Changes known to occur in the subchondral bone in osteoarthritis could alter transport into cartilage via this route and hence affect concentrations of oxygen and other important nutrients across the joint.